I'm far from an expert, have so far not yet even implemented a make up air implementation. I have only done some research on the subject. But I will give it a try. Someone with real knowledge should check what I say.

If you have a ventless, condensing dryer and no fireplace, you probably don't have to worry about backdrafting your furnace and boiler. Unless you have a very tight new construction home and very strong bathroom fans or a reasonably strong range hood. Then there is a chance but you would have to actually check to see if it does or not.

If your utility room is too tight, there is a chance that one appliance could backdraft the other if they have separate exhausts. For example, my HVAC furnace has powered exhaust and my hot water heater doesn't. If they had separate exhausts the furnace could over power the boiler exhaust.

What you more have to worry about is starving the furnace or boiler of air if it is not able to pull in enough if the room it is in is too tight. That would make them run inefficiently. Also, if not able to get enough combustion air, that could cause them to overheat since there may not be enough airflow to pull away the excess heat..

If the room isn't sealed too tightly and all appliances are properly installed and functioning well, you shouldn't have to worry about ant backdrafting.

Twintech Heating & Cooling

https://twintechheating.ca/